The present invention relates to magnetoresistive heads, examples of which are shown in U.S. Pat. Nos. 4,040,113; 4,141,051; 4,052,748; 3,848,217; 4,142,218; 3,979,775, 4.103,315; 4,315,291; 3,493,694; 3,405,355; 4,321,640; and 3,860,965.
Magnetoresistive heads include a strip-shaped element of a ferromagnetic, metallic, magnetically anisotropic material, for example NiFe, commercially known as Permalloy, which is deposited in a thin film on a substrate and positioned either with one of its edges in the immediate proximity of a magnetic recording medium, or alternatively, the element is positioned remotely from the medium with a flux guide arranged to bring the magnetic fields of the medium to the element. The fields of the recording medium produce variations in the magnetization of the element and thereby modulate the resistance of the element via the magnetoresistive effect. In order to measure the changing resistance of the magnetoresistive element, the element is electrically biased. This is typically done by directing an electric current through the element. Detection circuitry is then connected to the element so that the changing resistance of the element can be monitored to produce an output which is representative of the information stored on the medium.
A problem associated with prior art magnetoresistive heads has been the presence of Barkhausen noise in the output of the heads caused by the erratic movement of magnetic domain walls in the magnetoresistive element in response to the magnetic fields of the medium.
Another problem has been to ensure that the magnetic field generated by the bias current in the magnetoresistive element does not become so great as to alter the magnetically recorded data on the medium.